Process for cementing well bores

ABSTRACT

A process for cementing well bores is disclosed wherein high viscosity drilling mud in the area to be cemented is displaced by a liquid slug which in turn is displaced by a lower viscosity cement. The leading edge of the liquid slug has a viscosity substantially equal to or greater than the viscosity of the drilling mud during displacement thereof. The viscosity of the trailing edge of the liquid slug is substantially equal to or lower than the viscosity of the cement during displacement of the liquid slug.

O United States Patent 11s] 3,653,441 Tuttle 1 Apr. 4, 197 2 [54] PROCESS FOR CEMENTING WELL 3,299,952 1/1967 Savins 166/285 BORES I 3,411,580 11/1968 McKinney et a1... ..l66/285 3,525,397 8 1970 Dal ..I66 283 [72] inventor: Robert N. Tuttle, Houston, Tex. 3 532 168 1041970 i U l66/3{2 x [73] Assignee: Shell Oil Company, New York, NY.

Primary Examiner-Stephen J. Novosad [22] June 1970 Attorney-Harold L. Denkler and Theodore E. Bieber [21] App1.No.: 43,070

[57] ABSTRACT [52] US. Cl ..l66/291 A process for cementing wel] bores is disclosed wherein high [5 l] Int. Cl ..E2lb 33/14 vi o ity drilling mud in the area to be cemented is displaced [58] Field of Search ..166/283, 285, 291, 312 by a liquid Slug which in mm is displaced by a |ower viscosity cement. The leading edge of the liquid slug has a viscosity sub- [561 References Cited stantially equal to or greater than the viscosity of the drilling UNITED STATES PATENTS mud during displacement thereof. The viscosity of the trailing edge of the l1qu1d slug 1s substantlally equal to or lower than Williams the viscosity of the cement during displacement of [he 2,151,029 3/1939 Henst ..l66/312 l 2,326,577 8/1943 Teague et a1 ..166/312 X 3,193,010 7/1965 Bielstein ..166/285 10 Claims, 5 Drawing Figures 'lllll Win11 IHI a m H H Patented April 4, 1972 2 Sheets-Sheet l a. E Q

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ROBERT N. TUTTLE FIG. 5

FIG. 4

PROCESS FOR CEMENTING WELL BORES BACKGROUND OF THE INVENTION The difi'iculty of cementing a casing string in a bore hole has plagued the oil industry since its inception. One of the major problems known to the prior art is the difficulty in obtaining a satisfactory bond between the cement and the bore hole. This problem is most acute when the hole has been drilled with a high viscosity high density drilling liquid which is typically a barite weighted water or oil base mud having bentonite therein. Such drilling muds are capable of holding substantial amounts of cuttings in suspension which further increases the viscosity of the drilling mud, particularly near the bottom of the well bore.

' It is known in the industry that a common cause of poor cement bonds is that the injected cement does not satisfactorily displace the mud from around the casing but instead fingers or channels through the overlying body of drilling mud. See US. Pat. No. 2,848,051 and Journal of Petroleum Technology, Feb. 1967, p. 25l-260. As noted in the latter, numerous approaches have been taken to obviate the problem of bonding the cement to the bore hole wall. These include centering the casing string in the bore hole, scratching the bore hole wall, thinning the mud, isolating the cement by plugs during injection through the casing, establishing turbulence in the cement and using denser cement. As noted in the former, it has been suggested to displace the drilling of mud with a slug of liquid of greater viscosity than the drilling mud. Although considerable progress has been made in obtaining a reliable bond between the injected cement and the bore hole wall, it will suffice to note that more efficient and reliable cementing methods are highly desirable.

SUMMARY OF THE INVENTION It is an object of the invention to provide a cementing method which substantially reduces the occurrence of fingering or channeling of the cement through the drilling fluid.

Another object of the invention is to provide a cementing method using a high viscosity liquid slug to displace drilling fluid from the area to be cemented where the viscosity of the liquid slug is varied to provide more advantageous mobility ratios.

In summary, this invention contemplates a cementing process utilizing a slug of high viscosity liquid to displace the drilling fluid from the area to be cemented. The viscosity of the liquid slug, at least at the trailing end thereof, is lowered. Low viscosity cement is then used to displace the liquid slug from the area to be cemented and the cement is then allowed to set.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a typical poor cement job where the injected cement has significantly channeled through the drilling fluid;

FIGS. 2 and 3 show, respectively, an intermediate and final stage of a cementing process in accordance with one embodiment of the invention; and

FIGS. 4 and 5 show an intermediate and final stage of a cementing process in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a bore hole extending from the surface through a porous and permeable water bearing formation 12 and a porous and permeable hydrocarbon bearing formation 14. Extending into the bore hole 10 is conduit or casing string 16 having a cementing shoe 18 of any desired type on the lower end thereof. The annulus between the conduit 16 and the bore hole 10 is filled with a high viscosity high density drilling mud 20. During the typical prior art cementing process, a quantity of cement 22 is injectedthrough the casing 16 and exits through the cementing shoe 18 into the annulus. Typical oil field cement is of substantially lower viscosity than the drilling mud 20 and consequently channels or fingers therethrough leaving mud passages 24 communicating with the formation 14. It is apparent that when the casing 16 is perforated into the formation 14, substantial quantities of water from the formation 12 and drilling mud will be produced thereby impairing hydrocarbon production from the formation 14.

Referring now to FIGS. 2 and 3, there is shown a bore hole 30 extending from the surface through a water productive formation 32 and a hydrocarbon productive formation 34. A easing string 36 having a cementing shoe 38 thereon extends into a bore hole 30. The annulus between the conduit 36 and the bore hole 30 is filled with a high viscosity high density drilling liquid 40.

In accordance with this invention, a liquid slug 42 is injected through the conduit 36 and through the cementing shoe 38 to displace the drilling liquid 40 from the area to be cemented. As illustrated in FIG. 2, the liquid slug 42 comprises a leading end 44 in contact with the drilling liquid 40. It will be apparent that the continued injection of liquid through the conduit 36 will cause the leading end 44 of the slug 42 to displace the drilling liquid 40 from adjacent the area to be cemented.

For exemplary purposes, the liquid slug 42 is shown as comprising a drilling liquid displacing section 46, a viscosity adjusting section 48 and a cement compatible section 50. The viscosity of the trailing end 52 of the slug 42 has substantially the same viscosity as the cement slurry 54 adjacent thereto. A cementing plug 56 of any desired type is placed between the mud displacing section 46 and the viscosity adjusting section 48 during injection thereof into the casing string 36. In a similar manner, cementing plugs 58, 60 are positioned between the viscosity adjusting section 48, the cement compatible section 50 and the cement slurry 54. It will be apparent that the use of these cementing plugs substantially precludes intermingling of the separate sections prior to injection into the annulus. Continued injection of the cement slurry 54 through the conduit 36 is effected in any suitable manner, as by placing a cementing plug 62 in the conduit 36 at the trailing end of the cement slurry 54 and then injecting a liquid 64 into the conduit 36.

It will be appreciated that the cementing plugs 56, 58, 60 contact the cementing shoe 38 and allow subsequent liquids to pass therethrough. When the cementing plug 62 contacts the shoe 38, the passages between the interior of the conduit 36 and the well bore 30 are closed. The cement slurry 54 is then allowed to set.

The viscosity of the displacing section 46 is at least substantially as high as the viscosity of the drilling liquid 40. Consequently there is minimal fingering or channeling of the slug 42 into the drilling liquid 40 in the area to be cemented as shown in FIG. 2. Similarly, the viscosity of the cement compatible section 50 is at least substantially as low as that of the cement slurry 54 thereby avoiding substantial channeling of the slurry 54 into the slug 42 in the area to be cemented as shown in FIG. 3. It will be apparent to those skilled in the art that the most advantageous circumstance from a relative viscosity or mobility standpoint is where the viscosity of the displacing section 46 exceeds the viscosity of the drilling liquid 40 and where the viscosity of the cement compatible section 50 is less than the viscosity of the cement slurry 54.

It is preferred that the drilling liquid 40 be substantially completely displaced from the area to be cemented prior to passage of the viscosity adjusting section 48 into the bore hole 30 as shown in FIG. 2. This may be accomplished in any conventional manner, e.g., calculating the volume of the annulus from the bottom of the well bore 30 up to the top of the area to be cemented and then sizing the displacing section 46 to be somewhat in excess of the calculated volume.

It will be apparent that other prudent conventional cementing techniques, e.g., centering the conduit 36 in the well bore 30 and scratching the wall of the bore hole 30, are advantageously practiced in conjunction with this invention. In particular, the density of the cement slurry 54 is preferably equal to or greater than that of the liquid slug 42 which is in turn preferably greater than the density of the drilling liquid 40. By this technique, gravity induced channeling of the liquid slug 42 and the drilling liquid 40 is minimized. The composition of the liquid slug 42 may vary widely so long as certain general requirements, in addition to viscosity and density, are met. The liquid slug 42 should not substantially react with the conduit 36, the formations exposed by the bore hole or any filter cake accumulated thereon. The displacing section 46 should be inert with respect to the drilling liquid 40 and the viscosity adjusting section 48. The cement compatible section 50 should be inert with respect to the viscosity adjusting section 48 and to the cement slurry 54.

In a preferred embodiment of the invention, the displacing section 46 comprises a water-in-oil emulsion which is stabilized by the dispersion of small oil-wet acid-soluble solid particles therein. Such emulsions are described in greater detail in the copending application of H. C. H. Darley filed Dec. 26, I968, Ser. No. 787,139, now US. Pat, No. 3,525,397, and assigned to the assignee of this invention. Reference may be made to this application for a detailed description of the preferred emulsion.

In general, the preferred emulsion comprises diesel oil having a small proportion of tall oil therein such as Acintol Fa I made by Arizona Chemical Company, water or brine, a small amount of carbonate powder and an emulsifier such as Redicote E 11 made by Armour Industrial Chemical Company. The viscosity of this emulsion may be increased by decreasing the amount of diesel oil and increasing the amount of carbonate powder. The viscosity of the emulsion may be decreased by increasing the amount of diesel oil and decreasing the amount of carbonate powder. It will be seen that the viscosity of the displacing section 48 may be controlled to approximate or exceed the viscosity of the drilling liquid 40.

The viscosity adjusting section 48 comprises an acidic fluid, such as 15 percent hydrochloric acid with suitable corrosion inhibitors. When the section 48 is displaced into the bore hole 30, the acid dissolves the carbonate powder in the displacing section 46 thereby causing the emulsion to break into a water and an oil component. The viscosity of the mixed liquid components is substantially less than the viscosity of the emulsion. The breaking of the emulsion preferably occurs after the drilling liquid 40 is displaced from the area to be cemented.

The cement compatible section 50 preferably comprises brine which is weighted with any suitable substantially inert inorganic salt, such as sodium chloride, calcium chloride, zinc chloride or the like to provide a desired density. Such brines are inert with respect to the acid containing section 46 and to the cement slurry 54.

Referring to FIG. 3, it will be seen that the displacing section 46 and the viscosity adjusting section 48 have merged into a section 66 comprising the broken emulsion which is of substantially reduced viscosity. Because of the viscosity of the drilling liquid 40, significant fingering or channeling may occur thereinto. Since the viscosity adjusting section 48 is not injected into the bore hole 30 until the drilling liquid 40 has been substantially displaced from the area to be cemented, the fingering of the section 66 into the drilling liquid 40 is immaterial since it occurs outside of the area to be cemented. In the alternative, the drilling liquid may be completely displaced from the bore hole 30 prior to breaking the emulsion.

Other suitable compositions for the liquid slug 42 should be apparent to those skilled in the art. Other emulsions stabilized by acid or base soluble solid particles are practicable. In addition, chemically degradable aqueous polymer dispersions, such as acid degradable aqueous guar gum or hydroxyethyl cellulose dispersions are useable. Similarly, water degradable polymer dispersions such as polyoxyethylene or partially hydrolyzed acrylamide polymer dispersions are useable.

Referring now to FIGS. 4 and 5, there is shown a bore hole 68 extending from the surface through a formation 70. A case string 72 having a cementing shoe 74 thereon extends into the bore hole 68. The annulus between the conduit 72 and the bore hole 68 is filled with a high viscosity high density drilling liquid 76.

In accordance with another embodiment of this invention, a liquid slug 78 is injected through the conduit 72 and through the cementing shoe 74 to displace the drilling liquid 76 from the area to be cemented. As illustrated in FIG. 4, the liquid slug 78 comprises a leading end 80 in contact with the drilling liquid 76. The viscosity of the liquid slug 78 adjacent the leading edge 80 is substantially equal to or less than the viscosity of the cement slurry 84.

The viscosity of the liquid slug 78 is gradually decreased from the leading to the trailing ends thereof by modifying the composition of the liquid slug 78 as it is injected into the conduit 72. As shown in FIG. 5, the slug 78 displaces the drilling liquid 76 without substantial fingering. Similarly, the cement slurry displaces the slug 78 without significant channeling. Although the slug 78 decreases in viscosity from the leading edge 80 to the trailing edge 82, there is no substantial mixing of the slug 78 to cause drastic viscosity differences between the leading edge 80 and the drilling liquid 76 and between the trailing edge 82 and the cement slurry 84. This in fact is likely due to two causes. The first is that there are no sharp viscosity changes in the liquid slug 78 and the second is that the slug 78 has no immiscible sections or parts.

A preferred composition for use in the embodiment of FIGS. 4 and 5 is the oil-in-water emulsion previously described. The viscosity of this emulsion can be decreased by adding increasing amounts of diesel oil thereto. This may be accomplished in a convenient manner by preparing the emulsion immediately prior to injection into a flow line connected to the conduit 72 and adding increasing amounts of diesel oil during the process of making the emulsion. In the alternative, a batch of emulsion can be prepared having the maximum desired viscosity and passed through a flow line to the conduit 72. An increasing amount of diesel oil can be metered into the flow line to lower the viscosity of the emulsion.

It will be seen that there is provided a process for cementing well bores which efficiently displaces the drilling mud in the annulus and thereby aids in the creation of a good bond between the cement and the bore hole. It will be apparent that the disclosed technique may be used for cementing a conduit in a bore hole to provide a production well, an injection well or combination thereof. In addition to the previously described procedures for reducing the viscosity of the trailing edge ofa water-in-oil emulsion that is stabilized by acid-soluble particles, by contacting the emulsion with an acid and/or a mobile oil, such a viscosity reduction can also be effected by contacting the emulsion with the leading edge of the cement slurry and/or subjecting the emulsion to a relatively high temperature for a relatively long time in order to cause the breaking of the portion that is so treated.

I claim as my invention:

1. In a process for cementing a selected area in an annulus, between a conduit and a bore hole, filled with a high viscosity drilling liquid wherein a high viscosity liquid slug is injected into the annulus for contacting the drilling liquid and displacing the same from the selected area, the improvement comprising injecting a high viscosity liquid slug in which the viscosity at the leading edge is at least substantially as high as the viscosity of the drilling liquid during displacement thereof, and the liquid slug viscosity is capable of modification to a lower viscosity;

reducing the viscosity of the liquid slug at least adjacent the trailing end thereof to at least substantially as low as the viscosity of the cement slurry during displacement of the liquid slug by adding a viscosity modifying agent to the liquid slug;

injecting a cement slurry of lower viscosity than the drilling liquid into the annulus for contacting the trailing end of the liquid slug and displacing the liquid slug from the selected area; and

allowing the cement to set.

2. The process of claim 1 wherein the liquid slug, viscosity modifying agent and cement slurry are injected, in seriatim, through the conduit into the bore hole, the liquid slug comprises a degradable liquid and the viscosity modifying agent comprises a degrading agent.

3. The process of claim 2 comprising the step of segregating the degradable liquid from the degrading agent until the degrading agent enters the bore hole.

4. The process of claim 2 wherein the drilling liquid is substantially displaced from the selected area before the degrading agent enters the bore hole.

5. The process of claim 2 further comprising the step of injecting a cement compatible liquid slug into the conduit between the degrading agent and the cement for preventing contamination of the cement.

6. The process of claim 2 wherein the degradable liquid comprises a high viscosity emulsion and the degrading agent comprises a de-emulsifier.

7. The process of claim 6 wherein the emulsion comprises an oil-in-water emulsion having a continuous water phase and a discontinuous phase including oil-wet, acid-soluble solid particles and the de-emulsifier comprises an acid.

8. The process of claim 1 wherein the liquid slug and cement slurry are injected, substantially in seriatim, through the conduit into the bore hole, the liquid slug comprises a mu]- ticomponent liquid capable of viscosity reduction by changing the proportion of the viscosity modifying agent and the adding step comprises changing the proportion of the viscosity modifying agent as the liquid slug is injected into the conduit.

9. The process of claim 8 wherein the multicomponent liquid is an oil-in-water emulsion and the viscosity modifying agent comprises oil.

10. The process of claim 9 wherein the emulsion comprises a continuous water phase and a discontinuous phase including oil-wet solid particles. 

2. The process of claim 1 wherein the liquid slug, viscosity modifying agent and cement slurry are injected, in seriatim, through the conduit into the bore hole, the liquid slug comprises a degradable liquid and the viscosity modifying agent comprises a degrading agent.
 3. The process of claim 2 comprising the step of segregating the degradable liquid from the degrading agent until the degrading agent enters the bore hole.
 4. The process of claim 2 wherein the drilling liquid is substantially displaced from the selected area before the degrading agent enters the bore hole.
 5. The process of claim 2 further comprising the step of injecting a cement compatible liquid slug into the conduit between the degrading agent and the cement for preventing contamination of the cement.
 6. The process of claim 2 wherein the degradable liquid comprises a high viscosity emulsion and the degrading agent comprises a de-emulsifier.
 7. The process of claim 6 wherein the emulsion comprises an oil-in-water emulsion having a continuous water phase and a discontinuous phase including oil-wet, acid-soluble solid particles and the de-emulsifier comprises an acid.
 8. The process of claim 1 wherein the liquid slug and cement slurry are injected, substantially in seriatim, through the conduit into the bore hole, the liquid slug comprises a multicomponent liquid capable of viscosity reduction by changing the proportion of the viscosity modifying agent and the adding step comprises changing the proportion of the viscosity modifying agent as the liquid slug is injected into the conduit.
 9. The process of claim 8 wherein the multicomponent liquid is an oil-in-water emulsion and the viscosity modifying agent comprises oil.
 10. The process of claim 9 wherein the emulsion comprises a continuous water phase and a discontinuous phase including oil-wet solid particles. 